Mapper 的输入官方文档如下 The Mapper outputs are sorted and then partitioned per Reducer. The total number of partitions is the same as the number of reduce tasks for the job. Users can control which ke
Mapper 的输入官方文档如下 The Mapper outputs are sorted and then partitioned per Reducer. The total number of partitions is the same as the number of reduce tasks for the job. Users can control which ke
MapTask运行内部原理当map task开始运算，并产生中间数据时，其产生的中间结果并非直接就简单的写入磁盘。这中间的过程比较复杂，并且利用到了内存buffer来进行已经产生的部分结果的缓存，并在内存buffer中进行一些预排序来优化整个map的性能。如上图所示，每一个map都会对应存在一个内存buffer（MapOutputBuffer，即上图的buffer in memory），map会将
